phar.readonly can only be installed in PHP.INI
Their documentation says that it can be installed ini_set()("phar.readonly" 1 "PHP_INI_ALL"), but it cannot.
$ php -r "ini_set('phar.readonly',0);print(ini_get('phar.readonly'));"
1
Update http://php.net/manual/en/phar.configuration.php
php.ini - . phar.readonly php.ini, phar.readonly script . php.readonly php.ini, script " " INI, .